history has over 300 questions about “The history of Unix systems and their main components”. There's also historical-unix which has 24 questions but no usage guidance or tag wiki – which is also being used for the same purpose.
Pretty much any question about historical-unix would deserve the tag history, because it hasn't been a current product for decades. But the converse is not true. historical-unix has a distinct meaning and must stay.
Well, it's a proposed synonym now, though still needs some votes: